Screen grid tube



June 28,- 1932. B. VAN DER POL ET AL 1,865,065

- SCREEN GRID TUBE Filed Nov. 22. 1927 1&4 I 1292 139.5

INVENTOlS BALTHASAR VAN DER POL BY wig $20405 Mll L.

Patented June 2a, 1932- UNITED STATES PATENT; OFFICE;-

BALTHASAB VA! nil. POL AND KLAAS POBTHUIUS, OP'EINDHOVEN, m

BIGIOBB TO RADIO CORPORATION O! AURIGA, A"OORPO3A'1'ION OF nnnawscannnanm mm Application fled November 82, 1927, Serial 110, 285,017,and in the fletherlandl Iovember 18, me.

With high frequency am lification it is known to make use of tetro es,i. e. of discharge tubes comprising, as fourth electrode,

' a screening grid arranged between the anode and the'control grid. Thisscreening grid is maintained at a constant potential and serves tosubstantially neutralize the capacitive influence of the anode on thecontrol grid and vice versa. This internal capacity causes theamplification to become almost illusory at hig frequencies as the systemcommences to oscillate.

It is further possible to neutralize the said undesirable capacity stillmore perfectly by lengthening the screening, grid at both sides to someextent past the anode and the control grid and by providing thescreening grid at its two ends with shields which extend oversubstantially the whole internal section of the discharge tube, and,consequently, interce t substantially all of the electrostatic lines 0force between the anode and the control grid which possibly might runround the ends of the screening grid. Tubes constructed in this mannerpermit a high degree of amplification even with very short wavelengths.

The invention suggests another means whereby with discharge tubes havinga screening grid arranged between the anode and the control grid, thesame results can be obtained, said means consisting in the provision ofone or more metal shields which are insulated from the screening gridand which are conductively connected to a point having a potential whichdoes not oscillate, said shields being so shaped and arranged that anyelectrostatic line of force between the control grid and the anode hasto pass through the-screening grid.

Accordin to the invention, these shields should pre erably be connectedto. the filawhich are essential for the right comprehem,

sion of the invention.

Fig. l is a diagrammatic representation of ly. The control grid 4 isprovided at its both ends with insulating rings 5 and 6 respectively,for example of glass, which have sealed thereto metal disc-shapedshields 7 and 8 respectively. The diameter of these discshaped shieldsis slightly smaller than that of a screening grid 9, which is surroundedby or concentrically arranged with respect to anode 10. Owing to thepresence of the shields 7 and 8, which are conductively connected toeach other and to the pole wire 2 of the filament, the electro-staticlines of force between the control grid 4 and the anode 10 are compelledto pass through the screeninggrid 9, so that the above mentioned harmfulcapacitive effect is entirely avoided. The mutual connection between thetwo shields 7 and 8 may be established in any suitable manner, forexample by means of one or more conducting straps 12 running around the.screening grid 9 and the anode 10. I

The arrangement shown in Fig. 2 is quite identical to that in Figure 1but differs therefrom in that the insulating fastening rings 5 and 6 arenot sealed on to the control grid 4 but to the screening grid 9. In thiscase, too, thetwo disc-shaped shields 7 and 8 are connected to oneanother by one or more straps 12'whilst they are conductively connectedto the pole wire 2 of the-cathode.

With the arrangement of Fig. 3 the two disc-shaped shields 7 and 8 arenot attached to either of the two grids, but the shield 7 is carried andconductively connected to the filament by a small rod 11 which supportsthe middle of the filament 1 while the shield 8 is conductivelyconnected to the pole wire 2 of the cathode 1. The two shields haveconsequently a slightly different potential but since their potential isconstant, this does not alter the desired effect.

With the construction shown in Fig. 4, the two disc-shaped shields areconnected to one another not only electrically but also, by means pftwo-or more straps 12, so as to form a mechanical rigid unit, which isconductively secured to the pole wire 2 of the cathode 1 and which mayfurther be provided with one or more stiff supports 13, which can besealed in a known manner into the glass foot 14: of the tube. Anotherdifference with the above mentioned constructions consists in that theshields 7 and 8 have projections extending into the intermediate spacebetween the screening grid 9 and the anode 10 instead of into thatbetween the two grids. Also with this construction the harmful internalcapacity of the tube is nearly entirely counteracted.

Finally, Figure 5 shows a construction in which the disc-shaped shields7 and 8 are secured to the plate 10 so as to be insulated therefrom. Inthis case the shields are provided with cylindrical projections whichextend between the two grids, which still adds to the effect in view.The shield 8 is conductively connected to the pole wire 2 of the cathode1, and the two shields are electrically connected to each other by astrap 12.

With the type of tetrode under consideration, it is customary to leadout the cathode, the screening grid and the plate through the foot ofthe tube (Figs. 1, 2 and 3) and the control grid alone at the oppositeend of the tube.

Also when applying the invention, this con .struction will generally bepossible and recommendable. When, however, the anode isentirely-surrounded bythe shields 7 and 8 and strap 12 as indicated inFig. 4, in order to screen also the outer surface of the plate againstelectrostatic. lines of force of the leading-in conductors of thecontrol grid, it may be constructively more advantageous to lead out thecontrol grid at the same end as the cathode and the screening gridthrough the foot of the tube and to lead out the plate separately at theother end.

Under determined conditions the arrangement in accordance with theinvention may afford advantages over the known arrangement mentioned inthe beginning, because it is now possible to give the screening grid anydesired potential without influencing thereby the screen eifect. Withthe known construction the shields form part of the screening griditself or, at any rate, they are electrically connected thereto so thatpotential variations on the screening grid cause like potentialvariations on the shields.

It will be evident that the above mentioned constructions can bemodified in detail without. departing from the principle of theinvention. Thus, for example, the insulating rings 5 and 6 maysuccessfully be replaced by two or more insulating small blocks whichare arranged so as to be distributed over the circumference of thegrids.

Having now described our invention what we claim is:

1. An electron discharge tube comprising a cathode, a control gridsurrounding the cathode, a screen grid surrounding the control grid, ananode surrounding the screen grid, and shielding means comprising a pairof discs of conducting material substantially covering the ends of thescreen grid to shield thecontrol grid from electrostatic lines of forcefrom the anode, one of said discs being electrically connected to thecathode.

2. An electron discharge tube comprising a cathode, a control gridsurrounding the cathode, a screen grid surrounding the control grid, ananode surrounding the screen grid, and shielding means comprising a discof conducting material substantially covering one end of the screen gridand insulated. therefrom to shield the control grid from electrostaticlines of force from the anode, said disc being electrically connected tothe cathode.

3. An electron discharge tube comprising a cathode, a cylindricalcontrol grid surrounding the cathode, a cylindrical screen gridsurrounding the control rid, a cylindrical anode surrounding the screengrid, and shielding means comprising a pair of discs of conductingmaterial substantially covering the ends of the screen grid to shieldthe control grid from electro-static lines of force from the anode, saiddiscs being electrically connected to each other and to the cathode.

4. An electron discharge tube comprising a cathode, a cylindrical gridsurrounding the cathode, a cylindrical screen grid surrounding thecontrol grid, a cylindrical anode surrounding the screen grid, andshielding means comprising apair of discs of conducting material, eachdisc substantially covering one end of the screen grid and havin aportion. extending partly into the space between the anode and thescreen grid to screen the control grid from electro-static lines offorce from the anode.

5. An electron discharge tube comprising a cathode, a cylindrical gridsurrounding the cathode, a cylindrical screen grid surrounding thecontrol grid, a cylidrical anode surrounding the screen grid, andshielding means comprising a pair of discs of conducting material, eachdisc substantially covering one end of the screen grid and having aportion extending partly into the space between the anode and the screengrid to screen the control grid from electro-static lines of force fromthe anode, said discs being electrically connected to each other and tothe cathode.

6. An electron discharge tube comprising a cathode, cylindrical screengrid, control grid and anode electrodes concentrically mounted thereinand shielding means comprising a pair discs mounted adjacent to the ends.01: certain of said electrodes, each of said discs being provided witha-cylindrical portion extending partly into the space between two ofsaid electrodes to screen the control 'd from electrostatic lines offorce from t e anode, said discs being electricall connected togetherand to the oath e. 4

7. An electron discharge tube comprising a cathode, cylindrical screengrid, centre grid and anode electrodes concentrically mounted therein,and shielding means comprising a pair of discs mounted adjacent to theends of certain of said electrodes, each of said discs being rovidedwith a cylindrical portion extending partly into the space between theanode and the control grid to screen the control grid fromelectro-static lines of force from the anode, said discs beingelectrically connected together and to the cathode.

8. An electron discharge tube comprising a cathode, cylindrical screengrid, control grid and anode electrodes concentrically mounted therein,and shielding means comso prisin a of discs mounted adjacent to the en 0certain of said electrodes,-each of said discs being provided with acylindrical portion extending partly into the space between the anodeand the screen grid to screen the control grid from electro-static linesof force from the anode, said discs being electrically connectedtogether and to the oath-

